Field of the Invention
The present invention relates to a method and a user equipment performing measurement on a serving cell and one or more neighboring cells.
Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) is an improved version of a universal mobile telecommunication system (UMTS) and is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink. The 3GPP LTE employs multiple input multiple output (MIMO) having up to four antennas. In recent years, there is an ongoing discussion on 3GPP LTE-advanced (LTE-A) that is an evolution of the 3GPP LTE.
Micro cells, femto cells, and pico cells which provide small service regions are installed at particular locations within a macro cell which supports large coverage.
A user equipment, a typical example of mobile devices, moves easily, and service quality of a current cell may be degraded or a new cell providing a better service than the current one can be found from the movement. Therefore, the user equipment may move to the new cell found, which is called a user equipment's performing mobility.
Each cell supports fixed coverage and a user equipment can move at a variable speed within the scope of a wireless communication system. Therefore, frequency of the user equipment's performing mobility can vary depending on situations. To support mobility of a user equipment by taking into account the mobility state of the user equipment, a method for mobility state estimation (MSE) and a method for scaling mobile parameters have been used. By using the method, a user equipment can determine whether to report a measurement result, and mobility of the user equipment can be carried out on the basis of a measurement report. Therefore, the MSE and scaling of mobile parameters are closely related to carrying out mobility of a user equipment.
Meanwhile, a particular type of a wireless communication environment is in service, which comprises macro cells and small cells. Such a wireless communication environment can be called a heterogeneous network. In a heterogeneous network, a few of small cells can be defined within the coverage of a macro cell.
In an environment such as the above, if a user equipment moves around on the basis of a measurement report through the existing MSE and mobility parameter scaling, a problem such as a radio link failure (RLF) or a handover failure may occur. In this sense, there needs a measurement report method which can be carried out adaptively according to a mobility state of a user equipment and the type of a target cell in a communication environment where macro cells and small cells are coexistent.